The doodah on the end of the of the barrel is probably part of a muzzle reference system which detects and compensates for barrel droop at the muzzle due to gravitational pull and barrel heating due to firing.

The thing next to the barrel that looks like a coaxial machine gun is a coaxial 7.62 mm M240 machine gun.

Thanks, @jaytkay. I was thinking that it was a silencer—to the extent that it could be—to satisfy all those who demand that the killing noises be suppressed for environmental concerns or some such. Or to satisfy a silencer lobby that pressured the designer to add it.

.the coaxial is a less severe way to neutralize a target without using the main gun. It a “hot” environment it is a way to shoot without any of the crew needing to expose themselves outside the tank to use a machine gun. In the old days it was used to help aim the main gun at shorter distances since it is mounted in the same carriage as the big gun..

“The device on the end of the gun tube is the vehicle’s muzzle reference system. This allows the gunner and ballistic computer to account for droop in the main gun’s barrel caused by uneven heating. The thermal shroud on the barrel was intended to help alleviate this problem.”

@Jbor The grooves bite into the rounds and put a spin on them as they leave the barrel. Bullets need to spin in order to fly straight, like a football thrown spirally. It’s called rifling. Those large ribs in the suppressor is probably something to do with diverting gasses and flash.

On second thought that appears to be the mount where the actual machine gun goes. looks like the gun itself might not be mounted in that pic. When the tanks are in garrison the guns are locked away in an arms room for security reasons. There is never live ammo in them unless they are working a field problem, then if there are any fired rounds when it’s all over they get turned back in,

I think he means the grooves in the coax’s shroud @woodcutter. Those are there to help channel the muzzle flash away from the tank so the crew is not temporarily blinded. The flash suppressor doesn’t really suppress the flash, it just shields it from the crew.